Collaborative Research: Speleothem records of permafrost thaw and paleoclimate in the North American Arctic

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Given the possibility of substantial greenhouse gas release from thawing permafrost in a warmer future, as well as the threats to infrastructure from thawing permafrost, understanding the response of permafrost to past warmth is of fundamental importance. Speleothems (stalagmites and stalactites) only are expected to grow in Arctic caves when the overlying permafrost has thawed and no longer presents an impermeable barrier to seepage from the surface into the cave. This project will develop a record of when speleothems grew in Arctic caves and, consequently, under what past climatic conditions continuous permafrost thawed. The principal investigators will develop a website designed to educate lay audiences on how speleothems are used to study past climate. They will participate in the Cambridge Science Festival?s Science on the Street program, which provides an outlet for scientists to engage with public audiences attending community events on their research. This project will contribute to STEM workforce development by helping launch the research programs of three early-career scientists, as well as supporting the training of two graduate and three undergraduate students.The propose a novel approach to reconstruct past episodes of permafrost thaw ? dating cave speleothems from now-frozen areas, which require liquid water to grow and thus imply thawed ground conditions when they were deposited. Their work will take advantage of advances in uranium-thorium geochronology and use existing speleothem collections from three remote areas of Canada spanning 17° of latitude and isolated to continuous permafrost zones to document the extent of speleothem growth, and thus permafrost thaw, across variable interglacial conditions of the past 600 kyr ? some of which were warmer than today. They will also apply uranium-lead dating to a selection of samples to extend the dating range to millions of years. Well-dated, high-resolution records of terrestrial paleoclimate are also rare in the Arctic, though critical for understanding the response of this region to radiative forcings and determining the climate forcing that drove past changes in ice sheets, permafrost, sea ice, and vegetation. Therefore, they will measure stable isotope records along the speleothems to reconstruct climate variability over the intervals during which they grew. While likely fragmentary and confined to warm periods, these records will essentially provide underground extensions of the Greenland ice core ä18O record to numerous past interglacials.